Iron K_α Emission Lines in Seyfert(-Like) ActiveGalactic Nuclei: Revelation of a Rapidly Spinning Central Black Hole

Fe K_α lines are superimposed upon the x-ray continuum in most Seyfert(-like) active galactic nuclei (AGNs). By a data-fitting study, previous authors have claimed that the central black hole (BH) is either rotating or non-rotating according to the thin disk model. We develop the disk model to the torus model to determine the real spin of the BH. With formulations of the motion of both torus particles and photons near a BH in Kerr metric, we simulate iron emission lines from a thin luminous torus. It is found that only spinning BH galaxies can radiate observable profiles. The data-fitting to Fe lines of four AGNs observed by ASCA predicts that the central BH is spinning rapidly with the dimensionless specific angular momentum approaching the maximal value 1.